Small fixes in numpy.h (#2293)

- `PyArray_NewFromDescr_` should have been using `Py_intptr_t const *`
  - https://github.com/numpy/numpy/blob/18a6e3e505ee416ddfc617f3e9afdff5a031c2c2/numpy/core/src/multiarray/ctors.h#L5-L8
- `PyArray_GetArrayParamsFromObject_` should be using `NPY_BOOL`
  - https://github.com/numpy/numpy/blob/18a6e3e505ee416ddfc617f3e9afdff5a031c2c2/numpy/core/src/multiarray/ctors.c#L1350-L1355
  - https://docs.scipy.org/doc/numpy-1.13.0/reference/c-api.dtype.html#c.npy_bool
- `PyArray_DescrNewFromType` is at offset 96
  - https://github.com/numpy/numpy/blob/36e017194c32a53cf2965a513243cb3c348095df/numpy/core/code_generators/numpy_api.py#L141
- `array_t` constructor that takes a size and a pointer should take `ssize_t`.
  - Fixes #1599

include/pybind11/numpy.h

@@ -181,8 +181,9 @@ struct npy_api {
     unsigned int (*PyArray_GetNDArrayCFeatureVersion_)();
     PyObject *(*PyArray_DescrFromType_)(int);
     PyObject *(*PyArray_NewFromDescr_)
-        (PyTypeObject *, PyObject *, int, Py_intptr_t *,
-         Py_intptr_t *, void *, int, PyObject *);
+        (PyTypeObject *, PyObject *, int, Py_intptr_t const *,
+         Py_intptr_t const *, void *, int, PyObject *);
+    // Unused. Not removed because that affects ABI of the class.
     PyObject *(*PyArray_DescrNewFromType_)(int);
     int (*PyArray_CopyInto_)(PyObject *, PyObject *);
     PyObject *(*PyArray_NewCopy_)(PyObject *, int);
@@ -193,9 +194,10 @@ struct npy_api {
     PyObject *(*PyArray_FromAny_) (PyObject *, PyObject *, int, int, int, PyObject *);
     int (*PyArray_DescrConverter_) (PyObject *, PyObject **);
     bool (*PyArray_EquivTypes_) (PyObject *, PyObject *);
-    int (*PyArray_GetArrayParamsFromObject_)(PyObject *, PyObject *, char, PyObject **, int *,
-                                             Py_ssize_t *, PyObject **, PyObject *);
+    int (*PyArray_GetArrayParamsFromObject_)(PyObject *, PyObject *, unsigned char, PyObject **, int *,
+                                             Py_intptr_t *, PyObject **, PyObject *);
     PyObject *(*PyArray_Squeeze_)(PyObject *);
+    // Unused. Not removed because that affects ABI of the class.
     int (*PyArray_SetBaseObject_)(PyObject *, PyObject *);
     PyObject* (*PyArray_Resize_)(PyObject*, PyArray_Dims*, int, int);
 private:
@@ -211,7 +213,7 @@ private:
         API_PyArray_CopyInto = 82,
         API_PyArray_NewCopy = 85,
         API_PyArray_NewFromDescr = 94,
-        API_PyArray_DescrNewFromType = 9,
+        API_PyArray_DescrNewFromType = 96,
         API_PyArray_DescrConverter = 174,
         API_PyArray_EquivTypes = 182,
         API_PyArray_GetArrayParamsFromObject = 278,
@@ -866,7 +868,7 @@ public:
                 ExtraFlags & f_style ? f_strides(*shape, itemsize()) : c_strides(*shape, itemsize()),
                 ptr, base) { }
 
-    explicit array_t(size_t count, const T *ptr = nullptr, handle base = handle())
+    explicit array_t(ssize_t count, const T *ptr = nullptr, handle base = handle())
         : array({count}, {}, ptr, base) { }
 
     constexpr ssize_t itemsize() const {